Generation of characteristic fluorescence in a sample solution undergoing analysis requires the solution to be irradiated with a high intensity light beam of selected wavelength, often in the ultraviolet range. The source for this beam is typically a monochromator using a high intensity source such as an Xenon arc. However, the high radiation level, which is necessary for the high measurement resolution desired, when it is in the near ultraviolet, below 300 nm, tends to deteriorate the optical elements in the pre-slit condensing system of the exciting monochromator. In a relatively short time, typically a few hundred hours, the reflectivity of the mirrors drops off drastically, especially in the ultraviolet, with the formation of scattering films on their surfaces where the optical beam strikes. Also, some types of optical filters, if used, tend to solarize or lose their optical UV transmission. These problems further extend to the collimating mirrors and the grating of the monochromator. In addition, heat build-up at the entrance slit and in the monochromator may cause wavelength shift and band-width errors.
The interposition of a shutter between the source and the optical system is an effective remedy for the deterioration problem discussed above. Such a shutter is the subject of a related U.S. patent application Ser. No. 651,189 previously identified. The use of such a shutter can also be extended to further improvement in the life of the source engendered by reduction of source current when the shutter is closed.
It is an objective of our invention to provide means for reducing the source current when the shutter closes without causing interference with the computer function or accuracy.
It is a further object of our invention to increase the source life by such a reduction of source current.
It is also an object of our invention to reduce the heat generated in the lamp and power supply when the shutter is closed.
It is in addition an object to lower the temperature of the shutter and shutter motor when the shutter is closed.
It is also an object to accomplish the above without inducing instability or drift of the source lamp's output.